The present invention relates to a coating agent which is suitable for concealing grazes or scratches on glass surfaces such as repeatedly reusable colorless or pale transparent glass bottles. More particularly, the present invention relates to an emulsion composition whose principal ingredients are polydiorganosiloxane capable of forming an adhesive film on a glass surface at room temperature and polydiorganosiloxane which is liquid at room temperature, and a concealing agent to be applied to colorless or pale transparent glass bottles whose surfaces are grazed or scratched to form a film recovering a transparency.
Glass bottles used as containers for soft drinks, milk, etc. are usually collected after use and repeatedly reused. On the surface of such glass bottles, grazes are caused by the bottles contacting one another or contacting metal such as in machines utilized in the packing process or distribution. As the appearance of the bottles becomes less attractive by repeated reuse, the value of the packaged goods also apparently becomes lower.
To prevent the degradation of the appearance of the glass bottles several proposals have been made to form a graze-proof film or to form a concealing film for grazes. However, a satisfactory material has not been found because a variety of properties are necessary to form such graze-proof agents or concealing agents. Some properties which must be present simultaneously include:
(1) (a) For a graze-proof film: Excellent film strength under grazing conditions. PA0 (b) For a concealing film: Excellent concealing properties of the graze. PA0 (2) Good water resistance and no oil film formed on water when the coated bottle is dipped into water. PA0 (3) No change in the appearance of the bottle; no stickiness and no unusual lubricity due to the presence of the coating film. PA0 (4) Easy handling. PA0 (5) (a) Perfect removability by a bottle washing process utilizing an alkaline solution, or PA0 (b) resistance to a bottle washing process and no hindrance to the labeling or other process. PA0 (6) Safe for contact with the human body or foods. PA0 (7) No odor. PA0 (1) it is highly flammable and toxic due to the use of a solvent; PA0 (2) the film formed falls off irregularly during the bottle washing process; and, PA0 (3) the film becomes yellowish upon storage because of the large number of amino group-containing organic groups which are necessary for improving adhesiveness. PA0 (A) 100 parts by weight of polydiorganosiloxane having a viscosity of 10 to 100,000 cSt at 25.degree. C. in which 15 to 60 mole percent of an organic group bonded to a silicon atom is an organic group selected from the group consisting of a phenyl group, an aralkyl group and an alkyl group having carbon atoms of 6 or more, PA0 (B) 1 to 100 parts by weight of film-forming polyorganosiloxane comprising; PA0 (C) 1 to 30% by weight of a cationic surfactant or a surfactant mixture in which a part of the cationic surfactant is replaced with a nonionic surfactant based on the total amount of Components (A) and (B), PA0 (D) 60-1,000% by weight of water based on the total amount of Components (A) and (B),
Japanese Provisional Patent Publication No. 56040/1980 (which corresponds to U.S. Pat. No. 4,273,834) proposed such a concealing agent formed from a polyorganosiloxane resin containing methyl, phenyl and alkoxy groups bonded to silicon atoms. This concealing agent, however, is dissolved at a higher molecular weight stage only by hydrocarbon solvents such as toluene, xylene or gasoline. Therefore, it is not suitable for application to food containers from a standpoint of hygiene. When the concealing agent is made from a low molecular weight the polyorganosiloxane can be dissolved in ethanol so the foregoing problem is avoided, but there are disadvantages that expensive ethanol is required as the solvent, and that such as low molecular weight polyorganosiloxane resin results in a film having insufficient film strength and adhesiveness to glass so that the film formed falls off irregularly during the bottle washing process and thus causes a poorer appearance than an uncoated bottle.
An adhesive coating material in which the principal ingredient is polyorganosiloxane having siloxane units containing an amino group-containing organic bonded to the silicon atom to improve adhesiveness is described by Japanese Patent Publication No. 3627/1971, (which corresponds to U.S. Pat. No. 3,574,673) as a metal surface leveling agent. This coating material, however, has several disadvantages for purposes of the present invention:
Several latexes and emulsions of polyorganosiloxanes having functionality such as an amino group-containing group, a mercapto group-containing group and/or a trialkoxysilyl group to give an adhesiveness and/or form a cross-linked structure is proposed as a treating agent for fibers and the like in Japanese Provisional Patent Publication No. 131661/1979 (which corresponds to U.S. Pat. No. 4,228,054). However, when such a latex or emulsion is used for coating glass bottles, because its principal ingredient is a cross-linkable polyorganosiloxane, the film formed from the latex or emulsion having only these components by the effective ingredients falls off irregularly or the surface of the film becomes roughened by the bottle washing process. Additionally, when a tin compound is used as a catalyst accelerating the cross-linking, there is the disadvantage of toxicity.
The present inventors have previously made investigations concerning a concealing agent for grazes or scratches on glass bottles, and as a result, they have found that a concealing agent comprising a composition obtained by mixing an emulsion primarily comprising a polyorganosiloxane which is capable of forming a film having adhesiveness on glass surfaces at a room temperature and an emulsion primarily comprising a polydiorganosiloxane which is a liquid at room temperature could be removed by a washing process completely and it could sufficiently satisfy other requirements necessary for a concealing agent and thus overcome the above problems (Japanese Provisional Patent Publication No. 167449/1983 which corresponds to U.S. Pat. No. 4,467,068). While such an emulsion composition satisfies properties required for the aforesaid concealing agent for grazes or scratches, it remains a problem that a graze concealing effect is insufficient when a concealing agent for grazes or scratches which comprises a polyorganosiloxane of which all of or most parts of organic group bonded to silicon atoms are methyl groups has been applied to colorless or pale transparent glass bottles. Thus, it is preferred to apply them to conceal grazes or scratches on bottles of dark colors such as glass for beer containers or opaque glass, but it is restricted in appearance to use on colorless or pale transparent glass bottles such as glass for soft drinks or milk.